1. Field of the Invention
The present invention relates to a capsule and a process for the manufacture of the same. The present invention also relates to the use of a mass of the capsules in the manufacture of a magnetic body.
2. Description of the Related Art
The manufacture of permanent magnets using rare earth metal-based magnetic material particles is known. The manufacturing process involves shaping the magnetic material particles into a pre-fixed shape wherein the particles are held together by a polymer or the like. However, rare earth polymer-bonded magnets tend to experience durability issues especially due to the poor tolerance of the particles to oxidation at high temperatures which in turn, shortens the magnetic life-span of the magnets produced. In addition, the magnetic properties of the particles and therefore the magnetic body will be severely degraded with rapid oxidation of the magnet in air over time. Oxidation also occurs during the magnet manufacturing process which raises safety issues of this process.
To limit the durability problems caused by oxidation, the fabrication process of magnets may occur in static or non-oxidising surroundings or may involve a pre-compaction heat step to stop the particles from coming into contact with air.
In a known process, a magnetic body made of rare earth magnetic particles comes into contact with a mobile phase containing an anti-oxidant during or after the compaction step possibly via immersion of the magnetic particles in the said mobile phase. This approach has been found to minimise oxidation of the magnetic particles in the magnet manufacturing process by coating the surfaces of the magnetic particles that form the magnetic body with a protective layer. Although this may protect freshly exposed surfaces of the magnetic particles from oxidation at the time of or after compaction, it can be difficult to get all of the anti-oxidant to be evenly dispersed throughout the body of the magnet and thereby for the anti-oxidant to contact microfactures that may form in the magnetic particles during the compaction step. Microfractures in the particles may increase the susceptibility of particles to air and hence oxidation, especially when the liquid containing the anti-oxidant is unable to efficiently flow into the microfractures and coat the exposed surfaces within. Thus, the effectiveness of the exposure of the magnetic particles to the anti-oxidant during or after compaction step to minimise oxidation is reduced. As a result, a magnet made from the magnetic particles containing microfractures which have not been efficiently coated during or after the manufacturing process, may be susceptible to oxidation, which leads to a loss in its magnetic properties.
Accordingly, the challenge of preventing oxidation within the magnet at reasonable cost without comprising productivity and effectiveness remains. Given that oxidation problems exist in current magnetic manufacturing techniques, there is a need to improve the methods and materials used early on and throughout the magnet manufacturing process that overcome, or at least ameliorate, one or more of the disadvantages described above.
There is also a need to increase the contact surface area of the magnetic particles with the anti-oxidant during the manufacture of a magnetic body.